In general, on a substrate such as a semiconductor wafer or a liquid crystal substrate, there is formed a wiring for forming a circuit on a surface thereof. Such a wiring has been made of copper having a low electrical resistance and a high reliability instead of aluminum. However, as compared with aluminum, copper is easily oxidized. As a result, it is required to perform a plating process thereto with a metal having a high electromigration tolerance in order to suppress a surface of a copper wiring from being oxidized.
By way of example, a plating process is performed by supplying an electroless plating liquid to a surface of a substrate on which a copper wiring is formed. Such an electroless plating process is typically performed by a single-substrate processing apparatus (see, for example, Japanese Patent Laid-open Publication No. 2009-249679).